Scrolling Homecher on first/last page will no longer ignore events

Bug: 874202
Change-Id: I19db72345f8646ffa1100d2b51672990e12041e2
Reviewed-on: https://chromium-review.googlesource.com/1228998
Commit-Queue: Kevin Strohbehn <ginko@google.com>
Reviewed-by: Weidong Guo <weidongg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592256}

ash/app_list/pagination_controller.cc

@@ -68,13 +68,8 @@ bool PaginationController::OnGestureEvent(const ui::GestureEvent& event,
       float scroll = scroll_axis_ == SCROLL_AXIS_HORIZONTAL
                          ? details.scroll_x_hint()
                          : details.scroll_y_hint();
-      if (scroll == 0 ||
-          !pagination_model_->IsValidPageRelative(scroll < 0 ? 1 : -1)) {
-        // scroll > 0 means moving contents right or down. That is,
-        // transitioning to the previous page. If scrolling to an invalid page,
-        // do not handle this event.
+      if (scroll == 0)
         return false;
-      }
       pagination_model_->StartScroll();
       return true;
     }
@@ -82,6 +77,13 @@ bool PaginationController::OnGestureEvent(const ui::GestureEvent& event,
       float scroll = scroll_axis_ == SCROLL_AXIS_HORIZONTAL
                          ? details.scroll_x()
                          : details.scroll_y();
+      if (!pagination_model_->IsValidPageRelative(scroll < 0 ? 1 : -1) &&
+          !pagination_model_->has_transition()) {
+        // scroll > 0 means moving contents right or down. That is,
+        // transitioning to the previous page. If scrolling to an invalid page,
+        // ignore the event until movement continues in a valid direction.
+        return true;
+      }
       int width = scroll_axis_ == SCROLL_AXIS_HORIZONTAL ? bounds.width()
                                                          : bounds.height();
       pagination_model_->UpdateScroll(scroll / width);

ash/app_list/views/apps_grid_view.cc

@@ -1002,6 +1002,15 @@ void AppsGridView::OnGestureEvent(ui::GestureEvent* event) {
     return;
   }
 
+  // If the event is a scroll down in clamshell mode on the first page, don't
+  // let |pagination_controller_| handle it. Unless it occurs in a folder.
+  if (!folder_delegate_ && event->type() == ui::ET_GESTURE_SCROLL_BEGIN &&
+      !contents_view_->app_list_view()->IsHomeLauncherEnabledInTabletMode() &&
+      pagination_model_.selected_page() == 0 &&
+      event->details().scroll_y_hint() > 0) {
+    return;
+  }
+
   // Scroll begin events should not be passed to ancestor views if it occurs
   // inside the folder bounds even it is not handled. This prevents user from
   // closing the folder when scrolling inside it.